Key difference - autotrophs vs heterotrophs
Autotrophs and heterotrophs are two nutritional groups found in the environment. Autotrophs produce their own food through either photosynthesis or chemosynthesis. Autotrophs are at the primary level of the food chain. Therefore, both syntheses are referred to as primary synthesis. On the other hand, heterotrophs consume autotrophs or heterotrophs as their food. Thus, heterotrophs are located on the secondary or tertiary level of the food chain. The main difference between autotrophs and heterotrophs is that autotrophs are able to make organic nutrients from simple inorganic substances such as carbon dioxide, while heterotrophs cannot make organic compounds from inorganic sources.
This article explains
1. What are autotrophs - definition, characteristics, classification 2. What are heterotrophs - definition, characteristics, classification 3. What is the difference between autotrophs and heterotrophs?
What are autotrophs?
The organisms that make complex organic compounds such as carbohydrates, proteins and fats from simple compounds in the environment are known as autotrophs. This mechanism is known as primary production. They process photosynthesis or chemosynthesis. Both processes use water as a reducing agent. However, some autotrophs use hydrogen sulfide as a reducing agent. Autotrophs are considered to be the producers of the food chain. They do not need organic carbon as a living source of energy.
Classification of autotrophs
Autotrophs are either phototrophs or chemotrophs. Photosynthesis is a process in which carbon dioxide and water are used to produce sugar with the help of sunlight. Phototrophs convert the electromagnetic energy in sunlight into chemical energy by reducing carbon. During photosynthesis, autotrophs reduce atmospheric carbon dioxide and produce organic compounds in the form of simple sugars that store light energy. Photosynthesis also converts water into oxygen and releases it into the atmosphere. The simple sugar glucose is polymerized to form storage sugars such as starch and cellulose, which are long-chain carbohydrates. Proteins and fats are also produced through the polymerisation of glucose. Examples of phototrophs are plants, algae like seaweed, protists like euglena, phytoplankton, and bacteria like cyanobacteria.
In contrast, chemotrophs use electron donors from organic or inorganic sources as an energy source. Lithotrophes use electrons from inorganic chemical sources such as hydrogen sulfide, ammonium ions, iron ions, and elemental sulfur. Both phototrophs and lithotrophs use ATP, which is created during photosynthesis, or oxidized inorganic compounds, to produce NADPH by reducing NADP +, thereby forming organic compounds. Most of the bacteria such as Acidithiobacillus ferrooxidans, an iron bacterium, nitrosomonas, a nitrosifying bacterium, nitrobactor, a nitrifying bacterium, and algae are examples of chemolithotrophs.
Chemotrophs are mostly found on seabeds that sunlight cannot reach. A black smoker, a hydrothermal spring on the ocean floor that contains higher levels of sulfur, is a good source of sulfur bacteria.
What are heterotrophs?
Heterotrophs are organisms that are unable to bind inorganic carbon and thus use organic carbon as a carbon source. Heterotrophs use organic compounds produced by autotrophs such as carbohydrates, proteins, and fats for their growth. Most living organisms are heterotrophic. Examples of heterotrophs are animals, fungi, protists, and some bacteria. An overview of the cycle between autotrophs and heterotrophs is shown in Figure 3 .
Classification of heterotrophs
Two types of heterotrophs can be identified based on their energy source. Photoheterotrophs use sunlight for energy and chemoheterotrophs use chemical energy. Photoheterotrophs such as purple non-sulfur bacteria, green non-sulfur bacteria, and Rhodospirillaceae produce ATP from sunlight in two ways: bacteriochlorophyll-based reactions and chlorophyll-based reactions. Chemoheterotrophs can be either chemolithoheterotrophs, which use inorganic carbon as an energy source, or chemoorganoheterotrophs , which use organic carbon as an energy source. Examples of chemolithoheterotrophs are bacteria such as Oceanithermus profundus . Examples of chemoorganoheterotrophs are eukaryotes such as animals, fungi and protists. A flow chart for determining a species to be autotrophs or heterotrophs is shown in Figure 4.
Difference between autotrophs and heterotrophs
Autotrophs : Organisms that can produce organic nutrients from simple inorganic substances such as carbon dioxide are known as autotrophs.
Heterotrophs: Organisms that cannot produce organic compounds from inorganic sources and therefore depend on the consumption of other organisms in the food chain are known as heterotrophs.
Production of own food
Autotrophs : Autotrophs produce their own food.
Heterotrophs: Heterotrophs do not produce their own food.
Food chain level
Autotrophs : Autotrophs are at the primary level in a food chain.
Heterotrophs: Heterotrophs are found at the secondary and tertiary levels in a food chain.
Type of food
Autotrophs: Autotrophs produce their own food for energy.
Heterotrophs: Heterotrophs eat other organisms to get their energy.
Autotrophs: Autotrophs are either photoautotrophs or chemoautotrophs / lithoautotrophs.
Heterotrophs: Heterotrophs are either photoheterotrophs or chemoheterotrophs.
Autotrophs: Plants, algae, and some bacteria are the examples.
Heterotrophs: herbivores, omnivores, and carnivores are the examples.
Autotrophs and heterotrophs are two nutritional groups among organisms. The organisms that make complex organic compounds from simple compounds in the environment are known as autotrophs. Autotrophs are the producers of the food chain. Heterotrophs are unable to fix inorganic carbon and use organic carbon as a carbon source. They consume other organisms as food. The main difference between autotrophs and heterotrophs lies in their carbon source.
Reference: 1. "Autotroph". En.wikipedia.org. Np, 2017. Web. March 7, 2017.2. "Heterotrop". En.wikipedia.org. Np, 2017. Web. March 7, 2017.
Image courtesy: 1. “Fern” by Antony Oliver (CC BY 2.0) via Flickr 2. “Blacksmoker in Atlantic Ocean” by P. Rona - NOAA Photo Library (Public Domain) via Commons Wikimedia 3. “Auto-and heterotrophs” derivative by Mikael Häggström, below Use of originals by Laghi l, BorgQueen, Benjah-bmm27, Rkitko, Bobisbob, Jacek FH, Laghi L and Jynto (CC BY-SA 3.0) via Commons Wikimedia 4. “AutoHeteroTrophs flowchart” By Cactus0 - Own work (CC BY-SA 4.0) via Commons Wikimedia